JPH08262398A - Color liquid crystal display device - Google Patents

Abstract

PURPOSE: To embody a bright and highly colorful multicolor display by coloring light without using color filters and displaying plural colors with the same pixels and displaying white and lack B three primary colors of red, green and blue, which are the basis of the display. CONSTITUTION: Polarizing plates 21, 22 are arranged across a liquid crystal cell 10 formed by subjecting liquid crystal molecules to 90 deg. twist orientation and a reflection plate 20 is arranged on the rear surface side of the rear side polarizing plate 22. The transmission axis of the front side polarizing plate 21 is set in the direction of 130±5 deg. and the transmission axis of the rear side polarizing plate 22 in the direction of 140 to 160 deg. with the liquid crystal molecule orientation direction of the liquid crystal cell 10 on the rear surface side substrate 11. The value of Δnd of the liquid crystal cell 10 is set at 920±50nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device for obtaining a colored display without using a color filter.

[0002]

2. Description of the Related Art As a color liquid crystal display device capable of providing a colored display, one that colors light using a color filter is generally used. However, since this color liquid crystal display device uses a color filter to color light, it has a problem that the light transmittance is low and the display is dark.

This is due to the absorption of light by the color filter, and the color filter absorbs not only the wavelength light outside the wavelength band corresponding to the color but also the light in the wavelength band at a considerably high absorption rate. Therefore, the colored light that has passed through the color filter becomes light in which the light intensity is significantly reduced compared to the light in the wavelength band before entering the color filter, and the display becomes dark.

The liquid crystal display device has a transmissive type which uses the light from the backlight for display, and an external light (natural light, indoor illumination light, etc.) which is arranged on the back side. There is a reflection type that reflects and displays with a reflection plate, but when the above color liquid crystal display device is a reflection type, light that enters from the front surface side, is reflected by the reflection plate on the back surface side and is emitted to the front surface side is displayed. Since the light intensity is doubly reduced by passing through the color filter twice, the display becomes extremely dark and almost unusable as a display device.

Moreover, in the above color liquid crystal display device, since the display color of each pixel is determined by the color of the color filter corresponding to that pixel, in order to display many colors,
For example, it is necessary to obtain a desired display color by controlling the light transmission of each pixel by forming a set of three pixels corresponding to the color filters of the three primary colors of red, green and blue. The intensity of light is significantly weakened and the display color is dark.

On the other hand, as a conventional color liquid crystal display device for obtaining a colored display without using a color filter, an EC
A B-type (birefringence effect type) liquid crystal display device is known.
In this ECB type liquid crystal display device, a liquid crystal cell sandwiching a liquid crystal between a pair of substrates is sandwiched, and a polarizing plate is arranged on each of the front surface side and the back surface side of the liquid crystal cell. , The linearly polarized light that has passed through one of the polarizing plates and becomes incident light becomes elliptically polarized light with different polarization states due to the birefringence effect of the liquid crystal layer in the process of passing through the liquid crystal cell, and the other light The light incident on the polarizing plate of 1 and transmitted through the other polarizing plate becomes colored light having a color corresponding to the ratio of the light intensities of the respective wavelength lights forming the light.

That is, the ECB type liquid crystal display device is
Light is colored by utilizing the birefringence effect of the liquid crystal layer of the liquid crystal cell and the polarization effect of the pair of polarizing plates without using a color filter. Therefore, there is no absorption of light by the color filter. It is possible to obtain a bright color display by increasing the transmittance.

Moreover, in the above ECB type liquid crystal display device, the birefringence of the liquid crystal layer changes depending on the alignment state of the liquid crystal molecules according to the voltage applied between the electrodes of the two substrates of the liquid crystal cell, and accordingly the other birefringence is Since the polarization state of each wavelength light entering the polarizing plate changes, the color of the colored light can be changed by controlling the voltage applied to the liquid crystal cell, and therefore, the same pixel displays multiple colors. be able to.

[0009]

However, in the conventional ECB type liquid crystal display device, white and black which are the basics of display cannot be obtained, and red, green and blue which are the three primary colors of light can be displayed. Therefore, it is impossible to display full-color or multi-color with rich colors called multi-color.

According to the present invention, light can be colored without using a color filter, and a plurality of colors can be displayed by the same pixel. Moreover, white and black, which are the basics of display, and red,
It is an object of the present invention to provide a color liquid crystal display device capable of displaying three primary colors of green and blue to realize a clear and rich multicolor display.

[0011]

A color liquid crystal display device of the present invention includes a liquid crystal cell in which a liquid crystal is sandwiched between a pair of substrates having electrodes, and a liquid crystal cell sandwiched between the front surface side and the back surface side. A front side polarizing plate and a back side polarizing plate arranged, and a reflecting plate arranged on the back side of the back side polarizing plate,
In addition, the liquid crystal molecules of the liquid crystal cell are twist-aligned at a twist angle of approximately 90 ° from the rear surface side substrate of the liquid crystal cell to the front surface side substrate, and liquid crystal molecules on the rear surface side substrate of the liquid crystal cell. When the orientation direction of is the reference direction, the transmission axis or the absorption axis of the front side polarizing plate is deviated from the reference direction by 135 ± 5 ° in the direction opposite to the liquid crystal molecule twist direction viewed from the front side, The transmission axis or the absorption axis of the plate is deviated from the reference direction by 140 ° to 160 ° in the direction opposite to the twist direction of the liquid crystal molecules, the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell and the liquid crystal layer thickness d. The value of the product Δnd of and is set to 920 ± 50 nm.

[0012]

The color liquid crystal display device of the present invention utilizes external light and reflects the light incident from the front surface side by the reflection plate disposed on the back surface side for display. The incident light from the side is transmitted through the front-side polarizing plate to become linearly polarized light, the light is transmitted through the liquid crystal cell and is incident on the back-side polarizing plate, and the light transmitted through the back-side polarizing plate is reflected by the reflection plate, The light passes through the back-side polarizing plate, the liquid crystal cell, and the front-side polarizing plate in order, and is emitted to the front surface side.

In this liquid crystal display device, since the directions of the transmission axis or the absorption axis of the front and back polarizing plates are set as described above, the alignment direction of the liquid crystal molecules on the front surface side substrate of the liquid crystal cell is It is deviated obliquely to the transmission axis or the absorption axis of the front-side polarizing plate, and therefore a non-selected state in which no voltage is applied between the electrodes of the liquid crystal cell to vertically align the liquid crystal molecules (the liquid crystal molecules are in the initial twist alignment state) State), linearly polarized light that has entered through the polarizing plate is changed in polarization state by the birefringence action of the liquid crystal layer in the process of passing through the liquid crystal cell, and each wavelength light becomes elliptically polarized light with a different polarization state. The light that has become incident light and enters the back-side polarizing plate and that has passed through this back-side polarizing plate becomes colored light of a color corresponding to the ratio of the light intensities of the respective wavelengths that compose the light. Anti with reflector It has been emitted to the surface side of the liquid crystal display device.

When a voltage is applied between the electrodes of the liquid crystal cell, the birefringence action of the liquid crystal layer changes due to the change in the alignment state of the liquid crystal molecules due to the voltage, and the polarization of the light incident on the back side polarizing plate accordingly. Since the state changes, the coloring of the light changes according to the ratio of the light intensities of the light beams of the respective wavelengths that pass through this back-side polarizing plate, and the light is reflected by the reflector and emitted to the front surface side of the liquid crystal display device.

As described above, the color of the emitted light of this color liquid crystal display device, that is, the display color, changes depending on the voltage applied to the liquid crystal cell. If the twist angle of the liquid crystal molecules of the liquid crystal cell and the direction of the transmission axis or the absorption axis of the front and back polarizing plates are in the above-mentioned directions, and Δnd of the liquid crystal cell is in the above value, the liquid crystal cell 10 is displayed. The change in the display color that accompanies the change in the applied voltage of the above is a change including the three primary colors of red, green, and blue, and black and white.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view of a color liquid crystal display device of this embodiment. This liquid crystal display device includes a liquid crystal cell 10 and front side polarizing plates arranged on the front surface side and the back surface side of the liquid crystal cell 10. 21 and a back side polarizing plate 22, and a reflection plate 20 arranged on the back side of the back side polarizing plate 22. The reflection plate 20 is an omnidirectional reflection plate in which a metal film such as silver or aluminum is deposited on the surface of a base sheet made of a resin film or the like.

The liquid crystal cell 10 has transparent electrodes 13 and 14 made of an ITO film or the like, on which alignment films 15 and 16 are formed.
A pair of transparent substrates (for example, glass substrates) 11 on which
A nematic liquid crystal 18 is sandwiched between 12 and molecules of the nematic liquid crystal are twisted between the substrates 11 and 12, and the substrates 11 and 12 are bonded to each other via a frame-shaped sealing material 17. Is sealed in a region surrounded by the sealing material 17 between the two substrates 11 and 12.

The liquid crystal cell 10 is of an active matrix type using TFTs (thin film transistors) as active elements, for example, and a plurality of electrodes 13 formed on a substrate 11 on the back side thereof are arranged in rows and columns. The pixel electrodes, and the electrodes 14 formed on the substrate 12 on the front side are counter electrodes in the form of a single film facing all of the pixel electrodes 13.

Although not shown in FIG. 1, on the substrate 11 on which the pixel electrodes 13 are formed, a plurality of TFTs respectively connected to the pixel electrodes 13 and gate wirings for supplying gate signals to the TFTs in each row are provided. And data wiring for supplying a data signal to the TFTs in each column.

Further, the alignment films 15 and 16 provided on both the substrates 11 and 12 are horizontal alignment films made of polyimide or the like, and the alignment films 15 and 16 are subjected to alignment treatment (rubbing treatment) in directions substantially orthogonal to each other. The molecules of the liquid crystal 18 are regulated by the alignment films 15 and 16 in the alignment direction on both the substrates 11 and 12 (on the alignment films 15 and 16), and a slight pretilt with respect to the surfaces of the alignment films 15 and 16. In a state of being inclined at an angle, the two substrates 11 and 12 are twist-aligned at a twist angle of approximately 90 °.

FIG. 2 shows both substrates 11 and 12 of the liquid crystal cell 10.
It is the figure which looked at the liquid crystal molecule orientation direction and the direction of the optical axis (transmission axis or absorption axis) of each polarizing plate 21 and 22 from the front side of the liquid crystal display device in this example. , 22 are arranged with their transmission axes 21a, 22a oriented as follows.

As shown in FIG. 2, liquid crystal molecule orientation directions 11a and 12a on both substrates 11 and 12 of the liquid crystal cell 10 are shown.
Are substantially orthogonal to each other, and the liquid crystal molecules rotate clockwise (clockwise in the figure) when viewed from the front surface side from the rear surface side substrate 11 to the front surface side substrate 12, as indicated by the broken line arrow. It is twist-oriented at a twist angle of approximately 90 °.

When the liquid crystal molecule orientation direction 11a on the back surface side substrate 11 of the liquid crystal cell 10 is set to 0 °, the transmission axis 21a of the front side polarizing plate 21 is opposite to the liquid crystal molecule twist direction viewed from the front side. 13 in the direction (counterclockwise in the figure)
The transmission axis 22a of the back side polarizing plate 22 is in the direction of 5 ± 5 °
Is approximately 145 in the direction opposite to the twist direction of the liquid crystal molecules.
It is in the direction of °.

In the liquid crystal cell 10, the product Δnd of the refractive index anisotropy Δn of the liquid crystal 18 and the liquid crystal layer thickness d has a value of 920.
It is designed to be ± 50 nm. This color liquid crystal display device uses external light and reflects the light incident from the front surface side by a reflection plate 20 arranged on the back surface side to display the liquid crystal display device. 1
A display is driven by applying a voltage between the electrodes 13 and 14 of 1 and 12.

In this color liquid crystal display device, incident light from the surface side thereof passes through the front side polarizing plate 21 to become linearly polarized light, and the light passes through the liquid crystal cell 10 and enters the back side polarizing plate 22. The light transmitted through the back side polarizing plate 22 is reflected by the reflecting plate 20, and is sequentially transmitted through the back side polarizing plate 22, the liquid crystal cell 10 and the front side polarizing plate 21 and emitted to the front side.

Then, in a non-selected state (a state in which the liquid crystal molecules are in the initial twist alignment state) in which a voltage for rising and aligning the liquid crystal molecules is not applied between the electrodes 13 and 14 of the liquid crystal cell 10, the front side polarizing plate 21 is placed. The linearly polarized light that is transmitted and incident is changed in polarization state by the birefringence action of the liquid crystal layer in the process of transmitting through the liquid crystal cell 10, and each wavelength light becomes elliptically polarized light having a different polarization state, and becomes the backside polarization. Board 2
The light that has entered 2 and transmitted through this back-side polarizing plate 22 becomes colored light having a color corresponding to the ratio of the light intensities of the light components of the respective wavelengths, and the light is reflected by the reflection plate 20. The light is emitted to the front surface side of the liquid crystal display device.

The light reflected by the reflection plate 20 is subjected to birefringence by the liquid crystal layer of the liquid crystal cell 10 in the reverse order of the incidence in the process of exiting to the front surface side, and then enters the front surface side polarizing plate 21. Therefore, the light of the wavelength reflected by the reflection plate 20 passes through the front surface side polarization plate 21 and is emitted.

Further, when a voltage is applied between the electrodes 13 and 14 of the liquid crystal cell 10, the liquid crystal molecules are vertically aligned while maintaining the twist alignment state, and the birefringence action of the liquid crystal layer is changed by the change of the alignment state of the liquid crystal molecules. To do. The birefringence effect of the liquid crystal layer becomes smaller as the rising angle of the liquid crystal molecules becomes larger.

When the birefringence effect of the liquid crystal layer of the liquid crystal cell 10 changes, the polarization state of the light that passes through the liquid crystal cell 10 and enters the back side polarizing plate 22 changes accordingly. The coloring of the light changes according to the ratio of the light intensity of each wavelength light passing through 22, and the light is reflected by the reflection plate 20.
It is reflected by and is emitted to the surface side of the liquid crystal display device.

As described above, the color of the emitted light of this color liquid crystal display device, that is, the display color, changes depending on the voltage applied to the liquid crystal cell 10. The colors that can be displayed by one pixel of this color liquid crystal display device include all of the three primary colors of red, green, and blue, black that is a nearly achromatic dark display, and white that is a nearly achromatic bright display. .

That is, as in this embodiment, the twist angles of the liquid crystal molecules of the liquid crystal cell 10 and the directions of the transmission axes 21a and 22a of the front and back polarizing plates 21 and 22 are set as shown in FIG. , The value of Δnd of the liquid crystal cell 10 is set to 9
In the liquid crystal display device with a thickness of 20 ± 50 nm, the change in the display color due to the change in the voltage applied to the liquid crystal cell 10 is
The changes include red, green, blue, and black and white. Note that these display colors are obtained in the order of red → green → blue → black → white as the applied voltage to the liquid crystal cell 10 is increased.

Therefore, according to the above-mentioned color liquid crystal display device, light can be colored to obtain a bright color display without using a color filter, and a plurality of colors can be displayed by the same pixel. In addition to displaying white and black, which are the basics of display, the three primary colors of red, green, and blue are also displayed, so that a clear and rich multicolor display can be realized.

In addition, in the conventional ECB type liquid crystal display device, a liquid crystal cell having a large value of Δnd is used for displaying a plurality of colors. However, in the color liquid crystal display device of the above embodiment, the liquid crystal cell 10 is used. Liquid crystal molecule twist angle and polarizing plate 2
By setting the directions of the transmission axes 21a and 22a of the liquid crystal cells 1 and 22 and the value of Δnd of the liquid crystal cell 10 as described above, the above-mentioned colored light can be obtained. Therefore, the value of Δnd of the liquid crystal cell 10 is 920 ± 50 as described above
nm may be relatively small.

The fact that the value of Δnd of the liquid crystal cell 10 may be small means that one or both of the refractive index anisotropy Δn of the liquid crystal 18 and the liquid crystal layer thickness d can be made small, and the liquid crystal layer thickness d. Is smaller, the strength of the electric field applied to the liquid crystal layer is higher, and the viscosity of the liquid crystal having smaller Δn is low, so that the response becomes faster and the threshold voltage also lowers. For this reason, the color liquid crystal display device of the above-mentioned embodiment is different from the conventional ECB type liquid crystal display device in that
Multiple colors can be displayed with a low applied voltage.

Next, a second embodiment of the present invention will be described. In this example, in the color liquid crystal display device having the configuration shown in FIG. 1, the directions of the optical axes of the polarizing plates 21 and 22 are
The value of Δnd of the liquid crystal cell 10 is set as follows.

FIG. 3 shows the second embodiment, showing the alignment directions of liquid crystal molecules on both substrates 11 and 12 of the liquid crystal cell 10 and the optical axes (transmission axes in this embodiment) of the polarizing plates 21 and 22. It is the figure which looked at the direction from the surface side of the liquid crystal display device.

Also in this embodiment, the liquid crystal molecules of the liquid crystal cell 10 are arranged such that the twist direction of the liquid crystal molecules is right when viewed from the front surface side from the rear surface side substrate 11 to the front surface side substrate 12 as shown by the broken line arrow in FIG. Around (clockwise in the figure), the twist orientation is about 90 °.

In this embodiment, the liquid crystal molecule alignment direction 11a on the rear substrate 11 of the liquid crystal cell 10 is set to 0.
The transmission axis 21a of the front-side polarizing plate 21
Is set to 135 ± 5 ° in the direction opposite to the liquid crystal molecule twist direction viewed from the front side (counterclockwise in the figure), and the transmission axis 22a of the back side polarizing plate 22 is set in the direction opposite to the liquid crystal molecule twist direction. The direction is approximately 155 °. The value of the product Δnd of the liquid crystal cell 10 is 920 ± 50 nm, which is the same as in the first embodiment.

Further, in this embodiment, as the front side polarizing plate 21, a polarizing plate having a low degree of polarization with respect to light (blue component light) in the short wavelength region of the visible light region is used.
For 2, a polarizing plate with a normal degree of polarization is used. The average polarization degree of the front side polarizing plate 21 with respect to light in the visible light region is about 94%, and the average polarization degree of the back side polarizing plate 22 is about 99%.
Is.

Also in the color liquid crystal display device of the second embodiment, the change of the display color accompanying the change of the voltage applied to the liquid crystal cell 10 includes the changes of red, green, blue, and black and white. Therefore, it is possible to realize a clear and rich multicolor display.

Moreover, in this embodiment, a polarizing plate having a low degree of polarization for light in the short wavelength region of the visible light region is used as the front side polarizing plate 21 on which the incident light to the liquid crystal display device first enters. Therefore, it is possible to increase the incident amount of the light in the short wavelength range, that is, the light of the blue component, and display blue, which is difficult to be displayed as a display color, in a bright and clear color.

Although the display color described in each of the above embodiments is the color of one pixel, the color liquid crystal display device described above has a display color of a plurality of adjacent pixels in addition to the display color of each pixel. It is also possible to express those composite colors by combining

In each of the above embodiments, the directions of the transmission axes 21a and 22a of the front and back side polarizing plates 21 and 22 are shown in FIG.
Alternatively, although set as shown in FIG.
The direction of the transmission axes 21a and 22a of 22 may be the direction of the absorption axis.

Further, the directions of the optical axes of the polarizing plates 21 and 22 and the value of Δnd of the liquid crystal cell 10 are not limited to those in each of the above-mentioned embodiments, but the liquid crystal molecules on the rear side substrate 11 of the liquid crystal cell 10 are not limited. When the alignment direction 11a is set to 0 °, the transmission axis or the absorption axis of the front-side polarizing plate 21 is 135 ± 5 in the direction opposite to the liquid crystal molecule twist direction viewed from the surface side.
Direction, and the transmission axis or the absorption axis of the back side polarizing plate 22 is 140 ° to 160 ° in the direction opposite to the liquid crystal molecule twist direction.
And the value of Δnd of the liquid crystal cell 10 is 920 ±
Within the range of 50 nmno, it is possible to display white and black, which are the basics of display, and the three primary colors of red, green, and blue, and to realize a clear and rich multicolor color display.

Although the active matrix type liquid crystal cell 10 is used in the above embodiment, the liquid crystal cell 10 may be a simple matrix type or a segment type. Good.

[0046]

According to the color liquid crystal display device of the present invention, light is colored without using a color filter to obtain a bright color display, and a plurality of colors and achromatic white and black are formed in the same pixel. It is possible to display, and moreover, by displaying white and black which are the basics of display and the three primary colors of red, green and blue,
It is possible to realize a multicolor display that is clear and rich in color.

[Brief description of drawings]

FIG. 1 is a sectional view of a color liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the orientation of liquid crystal molecules on both substrates of the liquid crystal cell and the orientation of the optical axis of each polarizing plate.

FIG. 3 is a diagram showing a second embodiment of the present invention, which shows the orientation direction of liquid crystal molecules on both substrates of a liquid crystal cell and the orientation of the optical axis of each polarizing plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal cell 11a ... Liquid crystal molecule alignment direction on a back surface side substrate 12a ... Liquid crystal molecule alignment direction on a front surface side substrate 20 ... Reflector plates 21, 22 ... Polarizing plates 21a, 22a ... Transmission axis 23, 24 ... Phase difference plate 23a , 24a ... Slow axis

Claims (1)

[Claims] 1. A liquid crystal cell in which a liquid crystal is sandwiched between a pair of substrates on which electrodes are formed, and a front side polarizing plate and a back side polarizing plate which are arranged on the front side and the back side of the liquid crystal cell.
A liquid crystal molecule of the liquid crystal cell is twisted at a twist angle of about 90 ° from the back side substrate to the front side substrate of the liquid crystal cell. While being aligned, when the alignment direction of the liquid crystal molecules on the back side substrate of the liquid crystal cell is the reference direction, the transmission axis or the absorption axis of the front side polarizing plate is viewed from the front side with respect to the reference direction. The liquid crystal molecule twist direction is offset by 135 ± 5 ° in the opposite direction, and the transmission axis or the absorption axis of the back side polarizing plate is 140 ° to 16 degrees in the direction opposite to the liquid crystal molecule twist direction with respect to the reference direction.
A color liquid crystal display device, wherein the value of the product Δnd of the refractive index anisotropy Δn of the liquid crystal of the liquid crystal cell and the liquid crystal layer thickness d is set to 920 ± 50 nm.